The present invention relates to a method for the irreversible blocking of reactive Brönsted sites on the surface of an intraocular lens (IOL).
The protection of intraocular lenses against the sticking of substances originating from biological liquids, as well as medical adjuvants has been a demand in ophthalmology for some time. The materials for intraocular lenses are generally made of plastics based on PMMA (polymethylmethacrylate), silicone, and also based on other plastics. Most of these plastic materials have in common that they are selectively partially occupied with reactive sites due to the manufacturing process or the exposition to the environment, respectively. At these sites, substances originating from biological liquids, in particular proteins, are deposited as surface modifying substances in a mechanism which is not yet fully clarified. The interaction of proteins and solid state surfaces is particularly dependent on the functional groups in/at the surface. Among these sites are specifically also Brönsted sites (centres) (e.g. OH, COO), which may be determined for example by reflexion infrared spectroscopy. With the use of IR-microscopy OH-groups have been determined in/at PMMA lenses as well as in/at silicone lenses. Both materials do not show OH-groups in their ideal structure, but—as IR examinations haven proven—varying amounts of OH-groups are present in the real structure.
A further problem of the undesired occupancy of intraocular lenses with other substances is related to the removal of silicone oil adhesions, which can settle on the intraocular lens during a silicone oil tamponade.
Surface coating is a frequently used method to counteract such undesired depositions. With this, a continuous surface film coating is applied in different ways, which forms at least one monomolecular layer, as the following examples show.
U.S. Pat. No. 4,655,770 (briefly '770 in the following) describes the coating of an intraocular lens. The whole ocular lens made of PMMA is covered with a thin inert surface layer, after the surface has been provided with a relatively high concentration of hydroxyl groups by an ozone treatment. As a reagent for the passivation the reaction product of aminoethyl-N-aminopropyl trimethoxysilane and perfluordecanic acid was used in a ratio of 1:3, wherein the coupling of the fluorine compound onto the IOL occurs via a primary process, which calls for several coordinated chemical reactions and is only successful if the surface contains enough OH-groups, and so an ozone pre-treatment is added.
EP-B1-0 487 418 relates to an ophthalmalogical device, the surface of which having been fluorinated in a CF4-plasma, generated from tetrafluorocarbon and sulfur hexafluoride. During fluorination a change of the physical surface properties occurs, due to a complete chemical transformation of the surface regions.
Fluorine coated lenses currently marketed are chemically transformed by a CF4-plasma, compare for example EP-B1-0 487 418. With this, CH-bonds of the polymer are transformed into CF-bonds. As a result, one gets a “teflonised” lens having a low surface energy. With the plasma treatment, the roughness of the surface is decreased simultaneously.
During the plasma treatment several layers of atoms are chemically altered. In contrast to PMMA, silicone also comprises Si—O-bonds. These silicone-oxygen molecule parts may be transformed into the volatile SiF4. The evaporation of SiF4 interferes the formation of non-distorted protective layers or it contributes to an increase in roughness, respectively.
A further possibility is the immersion coating of PMMA lenses with “teflon-AF”, compare WO 92/10532. This polymeric perfluoro compound is dissolved in an inert solvent and is then distributed in the form of a thin layer on the surface by means of a immersion (dipping) process. After evaporation of the solvent, the teflon layer sticks to the surface by adhesion.
When using an immersion treatment with teflon-AF the surface of the applied coating must adhesively bind well. OH-groups being present in the silicone, which may be present for example because of the manufacturing conditions, complicate this process because of their hydrophilic nature.